1. Field of the Invention
The present invention relates generally to the field of front-end-of-the-line wet cleaning of a semiconductor wafer.
2. Discussion of Related Art
In semiconductor manufacturing, wet cleaning comprises a majority of the steps required to make a device. For many years, immersion cleaning has been the method of choice for wet cleaning. Due to the increasingly stringent requirements of wafer surface cleanliness, the limitations of such immersion cleaning are now being challenged.
In immersion cleaning, a batch of wafers may be dipped into a series of chemical and rinsing baths. Traditionally, the chemistry cleaning solutions are based on the RCA cleaning method: NH4OH/H2O2/H2O (or Standard Clean 1, SC-1) followed by HCl/H2O2/H2O (or Standard Clean 2, SC-2). SC-1 is most effective for cleaning particulate and organic contamination while SC-2 is very efficient for cleaning metallic contamination. In some cases HF precedes the sequence in order to etch or remove the oxide. The effectiveness of wet chemical cleaning is a function of the cleanliness of the overall cleaning system, which is in turn a function of the cleanliness of its sub-components, such as the carriers holding the wafers, the cleaning baths, and the transport environment.
A limitation of immersion cleaning is the build up of contamination during the useful life of the chemical bath by the particles removed from the wafers being cleaned. Inherently, immersion cleaning invites cross contamination between wafers as well as contamination of the chemical bath itself. The development and use of ultrapure materials, chemicals, and de-ionized (DI) water have allowed the extension of immersion cleaning methodology into many manufacturing lines. However, even using fresh chemicals for every batch, in addition to being very expensive, would not completely eliminate the issue of cross-contamination.
Consequently, single-wafer cleaning has become an alternative to batch cleaning. However, even single-wafer cleaning faces challenges. In a single-wafer spin cleaner, single wafers are cleaned in a horizontal orientation. Particles on the wafer are removed, in part, by applying cleaning chemicals and rinses to the surfaces of the wafer. However, during cleaning and rinsing, etched species or particulates tend to collide with the wafer surface causing particle defects. Hence, keeping the particles off the wafer surface is a challenge.